Genome-wide identification of fasciclin-like arabinogalactan proteins (FLAs) in melon and the role of CmFLA8 in glucose accumulation in fruit

Fasciclin-like arabinogalactan proteins (FLAs) play an important role in plant growth and development. Nevertheless, little is known about FLA genes in melon. Here, we conducted a systematic analysis of the FLAs subfamily within the annotated genome of melon (<italic>Cucumis melo</italic> L.). Thirteen FLAs were identified, and with sequencing analysis categorized into four groups based on the presence of FAS domains and AGP-regions. Notably, five of the CmFLAs proteins contain a glycosylphosphatidylinositol anchor signal. Promoter <italic>cis</italic>-element prediction analysis indicated that the majority of the <italic>CmFLAs</italic> family members respond to abiotic stresses and hormones. The RNA-seq and qRT-PCR assays showed that <italic>CmFLA10</italic> exhibited specific expression patterns in male flowers, while <italic>CmFLA12</italic> was highly expressed in the root tissue. Notably, most of the <italic>CmFLAs</italic> genes were expressed at high levels during the early stages of fruit development, subsequently declining as the fruit ripened. Their expression levels were negatively correlated with the total soluble solids content. Treatment with β-Glc Yariv inhibited the expression of <italic>CmFLA1</italic>, <italic>8</italic>, <italic>11</italic>, and <italic>13</italic>, resulting in a significant increase in the sugar content of the fruits. Expression analysis suggested an induced up-regulation of genes associated with sugar metabolism. Subcellular localization studies demonstrated that CmFLA8 was localized in the cytoplasm. Overexpression of CmFLA8 in melon fruit resulted in a decrease in glucose content. In this study, <italic>CmFLAs</italic> play a negative role in sugar accumulation and fruit ripening in melon, providing new insights into FLA gene functions.